An adjustable dockboard, as shown in U.S. Pat. 3,117,332, includes a ramp having its rear end hinged to a dock. The ramp is biased upwardly to an inclined position by a counterbalancing spring assembly and a manual releasable holddown device holds the ramp against elevation. Hinged to the front edge of the ramp is an extension lip which is adapted to swing from a pendant position, in which the lip hangs downwardly from the front edge of the ramp, to an elevated position in which the lip forms an extension to the ramp. The lip, when in the extended position, is adapted to engage the bed of a truck or carrier and bridge the gap between the ramp and the truck bed to enable material handling equipment to move between the dock and the truck.
In the dockboard, as disclosed in U.S. Pat. 3,117,332, the extension lip is automatically raised to its elevated position by the lip lifting and latching mechanism which is actuated by upward movement of the ramp when the holddown mechanism is released. In the pending U.S. patent application, Ser. No. 532,501 filed Dec. 13, 1974, the lip, instead of being raised to its elevated position as a consequence of upward movement of the ramp, is moved to its extended position as a consequence of downward movement of the ramp from the elevated position towards the cross traffic position. In either case, the engagement of the lip with the bed of the truck releases the weight of the lip from the lip latching mechanism, thereby releasing the lip latching mechanism, so that when the truck pulls away from the dock, the lip will automatically return to its pendant position.
If the ramp is below dock level when the truck pulls away from the dock, the ramp will remain at this downwardly inclined position unless the holddown mechanism is manually released to enable the counterbalancing spring assembly to raise the ramp. With the ramp elevated, the operator will then walk downwardly on the ramp until the ramp returns to its cross traffic position.
Occasionally, the operator may not carry out this procedure to return the ramp to dock level position with the result that the ramp remains in the downwardly inclined position. With the ramp in this below dock level position, it can provide an obstruction to material handling equipment moving over the dock.
U.S. Pat. 3,699,601 discloses a dockboard having a mechanism which will automatically return the ramp to a dock level position if the ramp is at a below dock level position when the truck pulls away from the dock. In that patent, control pawls are connected to the lip lifting mechanism and act to release the holddown mechanism as the lip pivots downwardly from the extended position towards the pendant position when the ramp is below dock level. Release of the holddown mechanism enables the counterbalancing spring assembly to pivot the ramp upwardly to the dock level position.